One-electron oxidation of nickel porphyrins. Effect of structure and medium on formation of nickel(III) porphyrin or nickel(II) porphyrin. pi. -radical cation. [Gamma radiation]

Journal Article · Thu May 30 04:00:00 EDT 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100164a046· OSTI ID:5890309

Nahor, G S; Neta, P ^[1]; Hambright, P; Robinson, L R ^[2]

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1. National Inst. of Standards and Tech., Gaithersburg, MD (United States)
2. Howard Univ., Washington, DC (United States)

The oxidation of several nickel(II) porphyrins by various radicals has been studied by pulse radiolysis in different media (Cl{sub 2}{sup {sm bullet}{minus}} and Br{sub 2}{sup {sm bullet}{minus}} in aqueous systems, Br atoms in organic solvents, and peroxyl radicals in organic and aqueous/organic systems). Photochemical oxidation was also examined in some cases. The absorption spectrum of the oxidation product was monitored within several microseconds after the pulse. Two types of differential spectra were observed, a broad absorption at 640-700 nm ascribed to the {pi}-radical cation, or a sharp absorption at 560-580 nm ascribed to nickel(III) porphyrin. Ni{sup II}TPP (tetraphenylporphyrin) in several organic solvents, protic and aprotic, was oxidized to Ni{sup III}TPP. The addition of 10% water as cosolvent or 0.1 M of electrolyte changed the route of oxidation to give the radical cation Ni{sup II}TPP{sup {sm bullet}+}. On the other hand, Ni{sup II}TSPP (tetrakis(4-sulfonatophenyl)porphyrin), which has four negative charges, was oxidized on the porphyrin ligand by all the radicals examined, in water and in several organic solvents. Ni{sup II}bis(N-methyl-4-pyridyl)diphenylporphyrin, with a charge of +2, and Ni{sup II} tris(4-sulfonatophenyl)(N-methyl-4-pyridyl)porphyrin, with an overall charge of {minus}2, were oxidized on the ligand in aqueous solution but on the metal in organic solvents. These and other results led to the conclusion that most radicals react with Ni{sup II}P by an inner-sphere mechanism to bind onto the metal and give the Ni{sup III}P form. However, when the porphyrin is sufficiently charged to repel the axially bound anion, and/or when the medium enhances the separation of this anion from the metal, the result is oxidation of the porphyrin {pi}-system. In all cases, however, the one-electron-oxidation products, whether Ni{sup II}P{sup {sm bullet}+} or Ni{sup III}P, decay to yield two-electron ring oxidation products.

• OSTI ID: 5890309
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:11; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400600 -- Radiation Chemistry
ABSORPTION SPECTROSCOPY
AQUEOUS SOLUTIONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BROMINE
CARBOXYLIC ACIDS
CATIONS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CHLORINE
COBALT 60
COBALT ISOTOPES
COMPLEXES
DATA
DECOMPOSITION
DISPERSIONS
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
EXPERIMENTAL DATA
FERMIONS
GAMMA RADIATION
HALOGENS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IONIZING RADIATIONS
IONS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LASER RADIATION
LEPTONS
MINUTES LIVING RADIOISOTOPES
MIXTURES
NICKEL COMPLEXES
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SOLVENTS
OXIDATION
PEROXY RADICALS
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHOTOLYSIS
PORPHYRINS
RADIATION EFFECTS
RADIATIONS
RADICALS
RADIOISOTOPES
RADIOLYSIS
SOLUTIONS
SOLVATED ELECTRONS
SOLVENTS
SPECTROSCOPY
STRUCTURE-ACTIVITY RELATIONSHIPS
TIME DEPENDENCE
TRANSITION ELEMENT COMPLEXES
YEARS LIVING RADIOISOT